The present invention relates to a storage controller and a controlling method therefor, particularly to a storage controller to which external storage controllers can be connected as externally-connected devices.
In database systems at a data center or similar, where a huge amount of data is dealt with, data is managed using storage systems that are configured separately from a host computer. A storage system is composed of, for example, one or more storage controllers. A storage controller is structured by arranging plural storage devices in arrays and configured based on, for example, the Redundant Array of Independent Inexpensive Disks (RAID) system. In a physical storage area provided by a storage device group, at least one or more logical volumes (logical units) are formed and provided to the host computer (or specifically, a database program operated on the host computer). The host computer transmits predetermined commands, thereby enabling the writing of data to, and the reading of data from, the logical volumes.
Lately, with the development of the information society, the amount of data that should be managed in a database is increasing and storage systems having higher efficiency and capacity have become desirable. Two major methods can be utilised for constructing a large-capacity storage system having high efficiency. One is a method for replacing existing small-capacity storage controllers with new, large-capacity storage controllers. For this method, a technique for transferring data in the database retained by the currently operating storage controllers to new storage controllers is disclosed in Japanese Unexamined Patent Publication No. H10-508967, Japanese Patent Laid-Open Publication No. 2001-337850, and Japanese Patent Laid-Open Publication No. H9-288547. The other method is to add a new storage controller to the existing storage systems. This method can be divided into two method types; one is a method for providing a new storage controller separately from the existing storage controllers; and the other is a method for connecting a new storage controller serially to the existing storage controllers.
Incidentally, Japanese Patent Laid-Open Publication No. 2001-337850 discloses a technique for managing storage areas of physical devices in sectors and dynamically configuring logical devices in sectors. Moreover, Japanese Patent Laid Open Publication No. H9-288547 discloses a technique for, when configuring logical devices with plural storage devices of different capacities, forming areas in accordance with a smallest capacity storage device and, for the remaining capacity, forming areas in accordance with a storage device that has the smallest capacity among the storage devices except for the smallest capacity storage device.